Bistable blocking oscillator



-A. D. SCAR BROU GH 2,676,251

BISTABLE BLOCKING OSCILLATOR April 20, 1954 Filed Dec. 1, 1950 OUTPUT I 35 swcnnomzme 1 WcoNTRoLL ms PULSE INPUT PULSE \NPUT I 1 I I 220 II E. 2 I1 G 4; sfucuaomzlm PULSE INPUT 42-7 1 svncuaomzmc, sYNcnRomzme PULSE INPUT 4 PULSE INPUT 22 22 J INVENTOR. 5 ALF-RED bficmzanoueu.

Patented Apr. 20, 1954 2,676,251 BISTABLE BLOCKING OSCILLATOR Alfred D.

signor to Hughes Tool Company,

Scarbrough, Los Angeles, Calif., as-

Houston, Tex.,

a corporation of Delaware Application December 1, 1950, Serial No. 198,703

8 Claims.

The present invention relates to a bistable "blocking oscillator, and more particularly to a bistable blocking oscillator whose oscillations may be started and stopped by gating pulses.

In conventional blocking oscillator circuits the oscillator bias is adjusted so that the circuit will not oscillate in the absence of synchronizing pulses, but is so near the oscillating position that the synchronizing pulses cause the circuit to perform a single oscillatory cycle following each synchronizing pulse. One method of starting "and stopping the oscillations is to insert a gating circuit and associated control circuitry in the lead supplying synchronizing pulses so that these pulses may be turned on or off at will. This method of performing the control function requires a plurality of tubes and many other components.

The present invention proposes to overcome these difficulties by employing a single tube which performs both the oscillating and gating func-- tions. The tube operates as a bistable blocking oscillator, that is, an oscillator having two degrees of stability. Once the oscillator is triggered by a positive controlling pulse, the oscillations will continue until the application of a negative controlling pulse.

v According to the present invention, a positive bias is obtained by rectification of a portion of the output of the oscillator during this oscillatory cycle, and this bias is applied to the grid of the oscillator in order to maintain the oscillations after the removal of the positive pulse.

In this manner, the oscillations will continue until the application of the negative pulse to the grid of the oscillator which effectivelyv cancels ,the positive bias produced by rectification. It is thus seen that the blocking oscillator of the presentinvention performs a series of oscillations, this-series stopped by a negative pulse. I

An object of the present invention is the provision of a bistable blocking oscillator which is started by impressing a positive pulse thereon'and stopped by impressing a negative pulse thereon.

A further object of the present invention is the provision of a bistable blocking oscillator which requires a low average current.

Still another object is to provide a bistable blocking oscillator which employs a single electron discharge tube for performing both the cscillatory and gating functions; i The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together being started by a positive 'pulsejanrl nected between anode l sistors l! and with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which several embodiments of the invention are illustrated by way of examples. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the invention.

Fig. 1 is a circuit diagram of one form of the present invention;

Fig. 2 is a diagram illustrating the input and output waveforms of the embodiment of Fig. 1;

' and Figs. 3 to 5 are circuit diagrams illustrating modifications of the synchronizing pulse input circuit of Fig. 1

Referring now to the drawings, wherein like reference characters designate likev or corresponding parts throughout the several views, there is shown in Fig. 1, which illustrates a preferred embodiment of the invention, an elecpolarity as shown in order to feed energy from the anode circuit back into the grid circuit. It is thus seen that tube It in conjunction with transformer 14 forms a conventional blocking oscillator.

transformer i4 is conand the positive terminal of a direct current power supply, not designated, the other terminal of the power supply being grounded. A pair of series connected re- IS are connected across the power supply, the junction point of resistors I! and I8 being connected to cathode I3 by means of conductor l8. Resistors Hand 18 constitute a voltagedivider for biasing cathode 13 positive with Primary winding. l5 of respect to ground, and therefore, with respect to grid [2 as set forth below. Resistor l3 preferably is made variable to permit initial adjustment of the positive bias normally impressed on cathode l3 when the blocking oscillator is in a quiet condition. A by-pass capacitor 2| is connected across resistor It to maintain the potential of cathode l3 at its proper level when the tube is renderedconductive, capacitor 2! being sufliciently large to keep the cathode potential constant during the oscillatory cycle of the oscillator.

Secondary winding [6 of transformer M has one end thereof connected to grid l2 by means of a conductor 22, the other end of winding [6 being connected to ground through a variable resistor 23 and a fixed'resistor 24. His thus seen that maintaining cathode I3 positive with respect to ground, by means of resistance-condenser combination l8-2l, provides a, normally negative grid bias since grid l2 normally is kept at ground potential by being connected directly to ground through secondary. winding [6 and resistors 23 and 24. A by-pass capacitor 25 is connected between resistor 23 and ground to form a low impedance path during the oscillation period of tube [0.

A storage capacitor 26 has its upper plate connected to grid 12 through resistor 23, winding I 6 and conductor 22, the lower plate of capacitor 25 being grounded. This connection, together withresistor iii, places capacitor 26 across the cathode grid circuit of tube Ill, thereby enabling capacitor 26 to appl a bias to grid 12. Synchronizing pulses 282, Fig. 2, are applied to capacitor 26 to charge the sam by means of a conductor 21 and a coupling capacitor 28. Controlling pulses 20E, 2lll are also applied to capacitor 26- by means of conductor 29.

In operation of the circuit thus far described, variable resistor I8 is adjusted so that the bias applied to grid I2 is suflicient to prevent oscillations even in the presence of synchronizing pulses 202. However, upon application of positivecontrolling pulse 200, capacitor 26 is charged to a higher positive level, with the result that the following synchronizing pulse 202 is of sufiicient magnitude to overcome the bias impressed on grid l2 and trigger the oscillator tubel 0.

Under these conditions, in the absence of an additional positive controlling pulse, oscillator tube it] would perform a single oscillatory cycle 253, since grid 12 normally is biased sufliciently negative to prevent any repetition of the oscillations. However, according to the present invention, additional biasing means is derived from the output of oscillator tube It and. this biasing means is applied to grid l2 to maintain the oscillations in the absence of a negative controlling pulse 28 I.

According to the preferred embodiment of the present invention, this self biasing of tube I is achieved by the provision of a unidirectional device, such as a rectifier 3|, having on end thereof connected to an auxiliary winding 32 of transformer M by means of conductor 33. Winding 32 also acts as the output circuit of tube Ill. The other end of rectifier-3i is connected to the upper plate of capacitor 26, so that positive pulses appearing at winding 32 charge capacitor 26. The charging of capacitor 23 by means of rectifier 3| during the oscillatory cycle of tube Ill serves to maintain the potential at grid I 2 sulficiently high so that the following synchronizing pulse 202 will trigger tube l0.

It is thus seen that the oscillations, once having been initiated by positive pulse 280 and the fOlIOWil'lg synchronizing pulse 202, will continue due to the additional biasing provided by rectifier 3|. The oscillations will cease only upon the application of a negative controlling pulse 29!, which neutralizes at least av portion of the positive. charge. on. capacitor. 26, and thereby renders grid I2 sufliciently negative so as to prevent further oscillations. In this manner, the circuit of the present invention provides a blocking oscillator for producing a series of oscillations which are started by a positive pulse and stopped by a negative pulse.

Although the circuit described depends upon the application of synchronizing pulses, it is apparent that it will operate without these pulses in a manner equivalent to a free running blocking oscillator. Thus, by proper adjustment of the circuit time constants and the bias on tube l0, oscillations will be initiated by positive pulse 200 and maintained by the bias from rectifier 3|, until the application of negative pulse 2!.

While only a preferred embodiment of the present invention has been described, it is clear that the disclosed circuit is capable of numerous modifications without departing from the spirit and scope of the invention. Thus, synchronizing pulses 282 may be impressed directly on rid l2 by means of a conventional coupling capacitor 34, as shown in Fig. 3; or they may be impressed upon anode ll by any suitable coupling capacitor 35, as shown in Fig. 4. It is also apparent that pulses 262 may be impressed on both anode H and grid lit by means of an additional transformer winding 36 coupled to winding l5, as shown in Fig. 5. Similarly, the biasing means may be obtained from portions of the circuit other than that described.

t is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A blocking oscillator circuit for producing a series of oscillations which are started by a positive pulse and stopped by a negative pulse, said circuit comprising: an electron-discharge device having a cathode, an anode, and a grid; a source of potential; means coupling said source between said anode and said cathode, said means including a first coil connected between said anode and said source; a second coil inductively coupled to said first coil and connected to said grid to feed back to said grid a portion of the voltage developed across said first coil; a capacitor coupled to said grid; means for applying synchronizing pulses to said capacitor; means for applying a positive pulse to said capacitor to increase the positive bias impressed onv said grid to a level making said oscillator responsive to the synchronizing pulse following said positive pulse, said synchronizing pulse setting said oscillator into oscillations; a rectifier magnetically coupled to said first coil for rectifying a portion of the voltage developed thereacross; means for supplying the output of said. rectifier to said grid to apply a positive bias thereto to maintain the oscillations produced .by said synchronizing pulses in the absence of a negative pulse; and means for applying a negative pulse to said capacitor to stop the oscillations.

2. A blocking oscillator circuit for producing a series of oscillations which are started by a positive pulse and stopped by a negative pulse, said circuit comprising: an electron discharge device having an anode circuit and a control grid circuit; means coupling said anode circuit to said control grid circuit for feeding back to said control grid circuit a portion of the energy developed in said anode circuit; a storage capacitor coupled to said control grid circuit .toapply a bias thereto; means for applying synchronizing. pulses. to said capacitor; means for applying positiveand negative pulses to said capacitor, the positive pulse being sufficient to enable the following synchronizing pulse to initiate the oscillations; a rectifier electrically coupled to said anode circuit for rectifying a portion of the output thereof and means for supplying the output of said rectifier to said control grid circuit to apply a positive bias thereto to maintain the oscillations in the presence of said synchronizing pulses and in the absence of the negative pulse.

3. A bistable blocking oscillator circuit comprising: an oscillator tube having an anode circuit and a control grid circuit; a storage capacitor coupled to said control grid circuit to apply a bias thereto; means for applying synchronizing pulses to said capacitor; means for applying positive and negative pulses to said capacitor, the positive pulse being sufficient to enable the following synchronizing pulse to initiate the oscillations; a rectifier electrically coupled to said anode circuit for rectifying a portion of the output thereof; and means for supplying the output of said rectifier to said control grid circuit to apply a positive bias thereto to maintain the oscillations in the presence of said synchronizing pulses and in the absence of the negative pulse.

4. A bistable blocking oscillator circuit comprising: an oscillator tube having an anode circuit and a control grid circuit; means for applying synchronizing pulses to said control grid circuit, said pulses being insufficient of themselves to initiate or maintain the oscillations of said tube; means for applying positive and negative pulses to said control grid circuit, the positive pulse being sufficient to enable the following synchronizing pulse to initiate the oscillations; a rectifier electrically coupled to said anode circuit for rectifying a portion of the output thereof; and means for supplying the output of said rectifier to said control grid circuit to apply a positive bias thereto to maintain the oscillations in the presence of said synchronizing pulses and in the absence of the negative pulse.

5. A bistable blocking oscillator circuit comprising: an oscillator tube having anode and control grid circuits; means for applying synchronizing pulses to said control grid circuit, said pulses being insufficient of themselves to initiate or maintain the oscillations of said tube; means for applying positive and negative pulses to said control grid circuit, the positive pulse being sufiicient to enable the following synchronizing pulse to initiate the oscillations; means electrically coupled to said anode circuit for rectifying a portion supplying the output of said rectifying means to of the output thereof; and means for said control grid circuit to apply a positive bias thereto to maintain the oscillations in the presence of said synchronizing pulses and in the absence of the negative pulse.

6. A bistable blocking oscillator circuit comprising: an oscillator tube having anode and control grid circuits; means for appl ing synchro nizing pulses to said control grid circuit, said pulses being insufiicient of themselves to initiate or maintain the oscillations of said tube; means for applying positive and negative pulses to said control grid circuit, the positive pulse being sufficient to enable the following synchronizing pulse to initiate the oscillations; and means electrically coupled to said anode circuit and responsive to the amplitude of the signal developed therein for applying a positive bias to said control grid circuit to maintain the oscillations in the presence of said synchronizing pulses and in the absence of the negative pulse.

7. In a blocking oscillator circuit whose oscillations are initiated but not maintained by a positive pulse and which includes an oscillator tube having anode and control grid circuits, apparatus for maintaining the oscillations in the absence of a negative pulse, said apparatus comprising: a rectifier electrically coupled to said anode circuit for rectifying a portion of the output thereof; and means for supplying the output of said rectifier to said control grid circuit to apply a positive bias thereto sufiicient to maintain the oscillations.

8. In a blocking oscillator circuit whose oscillations are initiated but not maintained by a positive pulse and which includes an oscillator tube having anode and control grid circuits, apparatus for maintaining the oscillations in the absence of a negative pulse, said apparatus comprising: means electrically coupled to said anode circuit for rectifying a portion of the output thereof; and means for supplying the output of said rectifying means to said control grid circuit to apply a positive bias thereto sufficient to maintain the oscillations.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,292,835 Hepp Aug. 11, 1942 2,468,420 Wendt Apr. 26, 1949 2,562,925 Lader Aug. 7, 1951 FOREIGN PATENTS Number Country Date 486,528 Great Britain June 3, 1938 

